Kidney stones are a significant medical problem, causing morbidity and entailing expenses due to emergency room visits, medications, and lithotripsy or other procedures. The long-term goal of this work is to produce an inhibitor of crystal deposition that would be suitable for testing in humans. The overall hypothesis of this work is that inhibitors of crystal attachment will be effective therapeutic agents in clinical nephrolithiasis. Specific objective are as follows: 1. To test molecules for the ability to inhibit calcium oxalate monohydrate (COM) crystal attachment to inner medullary collecting duct (IMCD) cells or to one another. We will test the anionic homopolymers poly(aspartic), poly(glutamic), and poly(acrylic) acids to determine the most effective inhibitors of COM crystal attachment to IMCD cells and to each other, using in vitro cell culture and aggregation assays, respectively. In addition, we will determine whether polymers with other anionic functional sites, poly(serine), the sulfated carbohydrates enoxiparin and pentosan, some sialie acid-containing oligosaccharides, and phosphorylated proteins and peptide homopolymers, have similar ef- fects on crystal attachment. 2. To test inhibitors of crystal attachment to cultured cells for their ability to ameliorate crystal deposition in ex- perimental animals. Polyanions and small to intermediate MW polymers containing other functional groups that may interfere with crys- tal attachment will be tested for their ability to inhibit calcium oxalate crystal deposition in rats treated with ethylene glycol and NH4C1 when administered using implanted osmotic minipumps. We will also determine the delivery to urine of effective inhibitors of calcium oxalate crystal retention by labeling compounds with fluorescent dyes or with biotin to permit detection. Renal function will also be measured in these animals to look for early renal toxicity. 3. To determine which of the inhibitors are effective when given orally. Inhibitors that are effective at preventing calcium oxalate crystal retention when administered using the implanted minipumps will be tested for their ability to inhibit crystal retention when given orally. Dosage regimens, feeding strategies, systemic medications, or accompany- ing agents will be employed as necessary to deliver adequate amounts of inhibitors via the oral route. 4. To determine whether the effective inhibitors have significant short and intermediate-term general and renal toxicity. Several inhibitors that are effective with oral dosing will be administered to rats at 5-10 times their effective doses for up to 180 days. Animals will be observed for general well being, and those that become sick or reach the end of the study period will have a complete battery of laboratory tests drawn. All ill animals and a selection of animals that appear healthy at the end of the study period will have necropsies performed. At the conclusion of this project, we expect to have three agents suitable for more comprehensive animal toxicity studies, presumably performed by a commercial laboratory with experience in satisfying FDA requirements. Should any of them be suitably free of toxicity, Phase I testing in human would be contemplated, presumably by a licensee.